Corrosion resistant alloy



Patented May 18, 1954 UNITED "PATENT OF F ICE .-..C.ORRO,SION. RESISTANT .ALLOY WilliamOZBirider and Claude'R. Bishop, Niagara .Falls; N. Y.,-as'sign0l's. to Union Carbide and ".CarbonCorporation, a corporation of New York No Drawing. Application December 10,4949,

- Serial No.- 132,426

4: Claims. 1(Cl; 75-122) This invention relates to ironrnickehmolybdenum alloys and refers more particularly to alloys of this type containing antimony and possessing excellent resistance to corrosionbyreducing acids together with good machinability.

Nickel-base alloys containing about. 10% to 40% molybdenum and a small proportion of iron, generally not exceeding about 5% to 20%" have enjoyed rather widespread use for many years by reason of their excellent resistance to corrosion in reducing acid media such as hot concentrated hydrochloric acid. However, a disadvantage of these alloys is their rather high cost which is due in part to their high content of expensive nickel and molybdenum and in part to the diificulty which is encountered in machining them, which .diificulty raises fabrication costs.

It is the principal-object of this invention to provide .iron-nickel-molybdenum alloys which combine the excellent corrosion resistance of the prior alloys with. greater machinability' and a lower proportion of expensive constituents.

This object is achieved by the inventionwhich is an alloy containing 30%to 70% iron; 11% .to 25% molybdenum; 0.25% to 3% antimonyy'the alloy of the present invention possesses corrosion resistance at least equivalent to that of the prior alloys in the same media.

' In the following tabletypical results of corrosion tests conducted on samples which were sand cast, heated hour at 1100 C. and air. cooled are set forth. In these tests the samples were weighed, immersed in boiling 10% hydrochloric acid for' 48 hours, removed, washed .and weighed and again immersed for 48 hours in the boiling acid. Each sample was thus tested forfive 48 hour periods and the corrosion rate calculated "and'reported as inches penetration per month.

- Table I figg g g gg i fi Corrosion Rate, Inch Penetration per Month First Second T-hird Fourth Fifth Mo 1 Sb 0 Period Period Period Period Period Average 29 Nil 0, 053 0. 00113 0. 00095 0.00145 0.0024 0. 0017 0. 00153 20- 20 Nil 0.039 0. 018 0.037 0. 043 0. 001 0. 067 0. 045 1 40 2 0. 006 0. 0165 0 00205 0. 0035 0. 00049 0. 0120 0. 0070 3 40 2 0. 009 0. 3045 0. 0073 0. 00024 0. 0047 0. 00049 0. 0043 remainder nickel and incidental impurities; the nickel content. being at -least.26%. A For severe conditions of service requiring a high degree of corrosion resistance and good ductility, it is preferred that the alloy of-the' invention contain to 50% iron; 2% to 20%molybdenurn; 0.25% to 3% antimony; the remainder nickel and incidental impurities, the nickel content being at least 45%. Up to 5% copper may be added'to the alloy with benefit, the copper addition improving resistance of the alloy to boiling dilute sulfuric acid. Aparticularly preferred range. ofxcomposition is 4%.;toj;8,%;molybdenum; to iron; up to"3% copper; 0.5%" to 2.5% antimony In. thetable. above thefirst two alloys are representative. of. the prior art and differ from each other .in that the second contains less molybdenum. and nickel andmoreiron than the first.

It will be observed that the second alloy is much table are representative of the alloy of the invention and diiTer from the first two compositions inthat they contain 2% antimony and have increased iron content and decreased molybdenum and nickel; contents. It will be observedvthat each v of 2 these compositions, exhibited greater average resistance to-the test 'medium than 'did 3 the second alloy in the table and compares very favorably with the first alloy in the table, some compositions showing even less attack than the first alloy.

In Table I, it will be noted, the antimony content of the compositions tested was held at 2% while the molybdenum, nickel and iron contents were changed. Another series of tests was made with varying antimony content and results of some of these tests are reported in Table II. The specimens were tested in the same condition of heat treatment as in the tests reported in Table I and the tests were conducted in the same way in boiling 10% hydrochloric acid.

chinability of the specimen. These tests indicate that the alloy of the invention has machinability of at least three times as great as that of conventional nickel-molybdenum-iron alloys. Furthermore the cutting edge of the tool showed no evidence of failure during the period of test on the alloy of the invention.

As is true of ferrous alloys in. general, carbon is an unavoidable impurity in the alloy of the invention. Care should be taken that the carbon content be as low as possbile. In accordance with good alloy-making practice, the alloy of the invention is deoxidized, conveniently with manganese and silicon, and the finished alloy may con- Table II g ggggi fg g Corrosion Rate, Inch penetration per month Percent Percent Percent First Second Third Fourth Fifth Aver 6 Mo S Period Period Period Period Period 1 Also contains 2% Cu.

oi 0.0078 inch penetration per month, whereas the corrosion rate of an alloy exactly similar except that it contained 2% copper (replacing 2% nickel) and 0.016% carbon showed an average (three 48 hour periods) corrosion rate of 0.00033 inch penetration per month in the same medium.

Tensile tests of the alloy of the invention have shown it to possess useful strength and ductility but indicate that for maximum strength.

and ductility the antimony content should not exceed 2%. cause excessive brittleness. The ductility of compositions containing not more than 2% antimony generally is greater than that of prior alloys free of antimony, as evidenced by elongation of tensile test specimens.

Although antimony of itself apparently has little eifect on the machinability of the alloy of the invention the alloy is significantly improved in machinability as compared to prior nickelmolybdenum-iron alloys presumably because of the present alloys increased iron content and lower molybdenum and nickel contents. Comparative machinability tests were made by machining cast samples of different compositions in conventional manner with conventional tools. The machining tests were continued on the conventional nickel-molybdenum-iron alloys until the cutting edge of the tool failed. The diameter of the specimen multiplied by the length of cut (expressed as D. L.) is a measure of the ma- More than 3% antimony tends to tain as impurities residual quantities of the deoxidizers used.

The alloys of the invention should be annealed after casting for optimum corrosion resistance. A satisfactory annealing heat treatment consists of heating the alloy about /2 hour at 1100" C. and air cooling. The cooling rate should be rapid enough to retain substantially the elevated temperature structure produced by annealing.

We claim:

1. An alloy containing 30% to 70% iron; 1% to 25% molybdenum; 0.25% to 3% antimony; up to 5% copper; the remainder nickel and incidental impurities, the nickel content being at least 26%.

2. An alloy containing 30% to 50% iron; 2% to 20% molybdenum; 0.25% to 3% antimony; up to 5% copper; the remainder nickel and incidental impurities, the nickel content being at least 45%.

3. A corrosion-resistant alloy containing 4% to 8% molybdenum; 35% to 45% iron; up to 3% copper; 0.5% to 2.5% antimony; the remainder nickel and incidental impurities, the nickel content being at least 45%.

4. A cast article required in its normal use to withstand corrosion by reducing acids, said article being composed of the alloy defined by claim 1.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,939,890 Frischer Dec. 19, 1933 2,054,927 Carius Sept. 22, 1936 2,219,445 Franks Oct. 29, 1940 2,222,473 Bishop Nov. 19, 1940 2,334,870 Franks Nov. 23, 1943 FOREIGN PATENTS Number Country Date 47,686 France Mar. 9, 1937 (Addition to 791,803) 

1. AN ALLOY CONTAINING 30% TO 70% IRON; 1% TO 25% MOLYBDENUM; 0.25% TO 3% ANTIMONY; UP TO 5% COPPER; THE REMAINDER NICKEL AND INCIDENTAL IMPURITIES, THE NICKEL CONTENT BEING AT LEAST 26%. 